UUIDs (Universally Unique Identifier) or GUIDs (Globally Unique Identifier) are defined in this document: [L1 ]
PT 8-Jul-2004: I have just added a UUID module to tcllib that implements type 4 uuids from the draft specification document. eg:
% package require uuid
1.0.0
% set id [uuid::uuid generate]
140d7c2c-4502-4144-6ae0-a4692e8ed819
% if {[uuid::uuid equal $id $id]} { puts "ids equal" }JMN 2005-11-26. On one of my windows machines - UUID version 1.0.0 calls to [uuid:uuid generate] take around 4.5 seconds to complete. This makes the function impractical for most uses. The delay seems to occur in a call to 'fconfigure <somesocket> -sockname'. I don't know if it's a peculiarity of my machine's network configuration or not - but even so it seems to me that this tcllib package should avoid calls that may take such a relatively long time.
Windows provides an API for generating GUIDs and some extensions make use of this, but I needed a pure-Tcl UUID generator. So, I came up with this. This proc, by no means, conforms to the standards discussed in the above document, but it does produce unique* identifiers that are good enough for me. :) Damon Courtney
proc uuid {} {
## Try and get a string unique to this host.
set str [info hostname]$::tcl_platform(machine)$::tcl_platform(os)
binary scan $str h* hex
set uuid [format %2.2x [clock seconds]]
append uuid -[string range [format %2.2x [clock clicks]] 0 3]
append uuid -[string range [format %2.2x [clock clicks]] 2 5]
append uuid -[string range [format %2.2x [clock clicks]] 4 end]
append uuid -[string range $hex 0 11]
return $uuid
}
proc guid {} {
## Return a GUID for Windows, which is just an uppercase UUID with braces.
return \{[string toupper [uuid]]\}
}
*JMN 2005-11-26 Note that the above 'guid' function does not produce unique values for quick successive calls.
e.g using the following script, you will most likely get the same value in a, b & c.
foreach {a b c} [list [guid] [guid] [guid]] {break}For a result that is more likely to be unique - you may want to add a call to [expr {rand()}] or similar.
I wrote a Windows C based Tcl extension for this (TclGetGUID) a few months back, and Pat helped by recommending the use of the Tcl C API call Tcl_UtfToUpper for converting a string to uppercase. The C source is really short and simple. It simply calls some underlying Windows APIs.
DKF: Don't forget to include planet and stellar system identifiers in that UUID... :^D
Category Glossary | Category Package distributed as a module in Tcllib